Sensitive low water emulsion explosive compositions

ABSTRACT

Cap sensitive emulsion explosive compositions comprising a discontinuous aqueous oxidizer salt phase, a continuous carbonaceous fuel phase, and closed cell void containing materials are disclosed which exhibit increased sensitivity, as measured by the 1/2 cartridge air gap sensitivity test, due to a reduced water content in the range of from about 4% to less than about 10% by weight of the emulsion matrix which is used to prepare the composition.

TECHNICAL FIELD

This invention relates to water-in-oil explosive compositions and, morespecifically, to cap sensitive emulsion explosives. In another aspect,this invention relates to emulsion explosive compositions havingincreased sensitivity resulting from low water content.

BACKGROUND ART

Water-in-oil emulsion type blasting agents were first disclosed by Bluhmin U.S. Pat. No. 3,447,978. These emulsion type blasting agents containan aqueous solution of inorganic oxidizer salts that is emulsified asthe dispersed phase within a continuous carbonaceous fuel phase, and auniformly distributed gaseous component. Later, cap sensitive emulsionexplosive compositions were produced using explosive additives such astrinitrotoluene, and pentaerythritol tetranitrate, (see e.g., U.S. Pat.No. 3,770,522). Water-in-oil emulsion explosive compositions have alsobeen made cap sensitive by the addition of nonexplosive detonationcatalysts (see e.g., U.S. Pat. Nos. 3,715,247 and 3,765,964). Mostrecently, cap sensitive water-in-oil emulsion type explosivecompositions, containing neither explosive ingredients nor detonationcatalysts, have been disclosed in U.S. Pat. Nos. 4,110,134, 4,149,916and 4,149,917.

While the cap sensitive emulsion explosive compositions disclosed in theabove-identified patents satisfy a wide range of requirements, there arecertain blasting applications in which even higher sensitivities thanare available using such compositions would be advantageous. Onerecognized indication of increased sensitivity is the standard halfcartridge air gap sensitivity test. Basically, this test measuressensitivity in terms of the length of the air gap across which one-halfof a standard cartridge of explosive material can detonate a second halfof a cartridge. Thus, for example, the preferred cap sensitive emulsionexplosive materials, prepared according to the disclosures of U.S. Pat.No. 4,110,134, have an "air gap sensitivity" of about two inches. Asnoted above, cap sensitive compositions having sensitivities greaterthan those of heretofore available cap sensitive explosive emulsioncompositions are desirable in certain blasting applications.

SUMMARY OF THE INVENTION

It has been discovered that by lowering the water content of the matrixof water-in-oil emulsion explosive compositions to below about 10%, theexplosives, which basically comprise a continuous hydrocarbon phase, adiscontinuous aqueous phase containing inorganic oxidizing materials,and closed cell void containing materials, attain increased explosivesensitivity. The compositions of the present invention comprise anemulsion matrix having from about 3.5% to about 8% by weight of thehydrocarbon fuel including an emulsifier; from about 4% to less thanabout 10% by weight of water; and from about 65% to about 85% by weightof inorganic oxidizing salt. To such materials are added from about0.25% to about 15% by weight of closed cell void-containing materials;and, optionally, up to about 5% by weight nonexplosive detonationcatalysts, up to about 20% lower alkylamine or alkanolamine nitratesensitizing agents and up to about 20% by weight auxiliary fuels to formthe explosive emulsion.

DETAILED DESCRIPTION OF THE INVENTION

Thus, quite unexpectedly, it has been discovered that cap sensitiveexplosive emulsion compositions detonable by a number 6 cap at diametersof 1.25 inches and less can be substantially increased in sensitivity,as measured by the half cartridge air gap test, by reducing the watercontent of the matrix to below about 10%. The compositions of thepresent invention do not employ conventional high explosive sensitizers,are water resistant because of their emulsion characteristics,insensitive to initiation by fire, impact, friction or staticelectricity, exemplify good low temperature detonation characteristicsand are stable enough for commercial utilization.

As used herein, the term "matrix" and/or "emulsion matrix" is defined asthe water-in-oil emulsion including fuel, emulsifiers, water andinorganic oxidizing salts but excluding closed cell void-containingmaterials and auxiliary fuels (such as aluminum for example). Thus, Ihave discovered that by employing less than 10% by weight water in theemulsion matrix, the sensitivity of the emulsion explosive compositionitself (prepared by admixing closed cell void-containing materials and,optionally, sensitizing agents with the matrix) is unexplainablyincreased.

The water-in-oil explosive emulsions of the present invention comprise,as a continuous phase thereof, from about 3.5% to about 8.0%, andpreferably from about 4.5% to about 5.5% by weight of a carbonaceousfuel component, including an emulsifier. The carbonaceous fuel componentcan include most hydrocarbons, for example, paraffinic, olefinic,naphthenic, aromatic, saturated or unsaturated hydrocarbons. In general,the carbonaceous fuel is a water immiscible emulsifiable fuel that iseither liquid or liquefiable at a temperature up to about 200° F., andpreferably between about 110° F. and about 160° F. At least about 2.0%by weight of the total composition should be either a wax or oil, or amixture thereof. If a mixture of wax and oil is employed, the waxcontent can preferably range from about 1.0% to about 3.0% by weight andthe oil content can range from about 3.0% to about 1.0% by weight(depending on wax content) of the total emulsion.

Suitable waxes having melting points of at least about 80° F. such aspetrolatum wax, microcrystalline wax, and paraffin wax, mineral waxessuch as ozocerite and montan wax, animal waxes such as spermacetic wax,and insect waxes such as beeswax and Chinese wax can be used inaccordance with the present invention. Examples of preferred waxesinclude waxes identified by the trade designations INDRA such as INDRA5055-G, INDRA 4350-E, and INDRA 2119 sold by Industrial Raw MaterialsCorporation. Also suitable is ARISTO 143° sold by Union 76. Othersuitable waxes are WITCO 110X, WITCO ML-445, and X145-A, which aremarketed by Witco Chemical Company, Inc. The most preferred waxes are ablend of microcrystalline waxes and paraffin, such as the wax sold underthe trade designation INDRA 2119, identified above. In this regard, moresensitive emulsions can be obtained by using a blend of microcrystallinewax and paraffin rather than microcrystalline or paraffin wax alone.

Suitable oils useful in the compositions of the present inventioninclude the various petroleum oils, vegetable oils, and various gradesof dinitrotoluene; a highly refined white mineral oil sold by WhitcoChemical Company, Inc. under the trade designation KAYDOL and the like.

The carbonaceous fuel component of the subject invention will alsoinclude the emulsifier used to form the emulsion explosive composition.Any of a wide variety of water-in-oil emulsifiers can be employed andthe following examples are not to be interpreted as limiting. Thus,suitable emulsifiers which can be employed in the emulsion explosives ofthe present invention include those derivable from sorbitol byesterification with removal of one molecule of water such as sorbitanfatty acid esters, for example, sorbitan monolaurate, sorbitanmonooleate, sorbitan monopalmitate, sorbitan monostearate, and sorbitantristearate. Other useful materials comprise mono- and diglycerides offat-forming fatty acids, as well as polyoxyethylene sorbitol esters,such as polyethylene sorbitol beeswax derivative materials andpolyoxyethylene(4)lauryl ether, polyoxyethylene(2)ether,polyoxyethylene(2)stearyl ether, polyoxyalkylene oleate, polyoxyalkylenelaurate, oleyl acid phosphate, substituted oxazolines and phosphateesters, mixtures thereof and the like. In general, the emulsifiersshould be present in an amount ranging from about 0.5% to about 2.0% byweight of the total composition, and preferably from about 0.8% to about1.2% by weight of the total composition.

The discontinuous aqueous phase of the explosive emulsions of thepresent invention are unusual in that they contain less than about 10%by weight of the emulsion matrix of water. Thus, the emulsion matrixesof the compositions of the present invention contain a minimum of about4.0% water, less than about 10% by weight water and preferably fromabout 6% to about 8% water. The precise amount of water employed willdepend, to some extent, upon the mixture of inorganic oxidizing saltswhich are employed.

The inorganic oxidizing salts dissolved in this unusually low amount ofwater will generally comprise from about 65% to about 85% by weight ofthe emulsion explosive composition. A major proportion of the inorganicoxidizing salt content is preferably comprised of ammonium nitrate;however, mixtures of ammonium nitrate and other alkali and alkalineearth metal nitrates as well as alkali and alkaline earth metalperchlorates can be successfully employed as the inorganic oxidizingsalt components of the emulsions of the present invention. Preferredinorganic oxidizing salts, in addition to ammonium nitrate, includesodium nitrate and sodium perchlorate. However, other nitrates andperchlorates, for example calcium nitrate, calcium perchlorate,potassium nitrate and potassium perchlorate can also be used.

The adjustment of the kinds and amounts of inorganic oxidizing salts toobtain an aqueous oxidizing salt solution phase for the emulsion matrixwhich contains reduced amounts of water is an important part of thesubject invention. Especially preferred mixtures of inorganic oxidizingsalts include from about 55% to about 70% ammonium nitrate incombination with from about 5% to about 20% sodium nitrate and up toabout 10% ammonium or sodium perchlorate. Those skilled in the art willrecognize that because of the varying solubility characteristics ofsuitable inorganic oxidizing salts such as, for example, ammoniumperchlorate as compared to ammonium nitrate, adjustment of water contentwithin the range specified may be necessary according to the particularmix of inorganic oxidizing salts employed.

Thus, both the mix of inorganic oxidizing salts and the precise watercontent below about 10% by weight of the emulsion matrix are variableswhich can be adjusted to achieve the increased sensitivity of thecompositions of the subject invention.

In addition to the above-identified carbonaceous fuel phase and aqueousoxidizer solution phase, explosive emulsions of the present inventionpreferably include sensitizing agents selected from three categories.The first two categories of sensitizing agents, and mixtures of them canbe employed in amounts ranging from about 0% to about 20% by weight ofthe total explosive emulsion composition. The first category ofsensitizing agents are lower alkylamine and alkanolamine nitrates suchas methylamine nitrate, ethylamine nitrate, ethanolamine nitrate,propanolamine nitrate, ethylenediamine dinitrate, and similar aminenitrates having from about one to about three carbon atoms. Thepreferred amine nitrate sensitizing agent for the emulsions of thepresent invention is ethylenediamine dinitrate. The second category ofsensitizing agents are nonexplosive compositions which can be describedas detonation catalysts. These detonation catalysts include inorganicmetal compounds of atomic number 13 or greater, other than groups 1A and2A of the periodic table and other than dioxides. Preferable detonationcatalysts include compounds of copper, zinc, iron, or chromium, as theseproduce the greatest increase in sensitivity. Compounds of aluminum,magnesium, cobalt, nickel, lead, silver and mercury are also suitable.For the purpose of this invention, silicon and arsenic are notconsidered to be metals. Nitrates, halides, chromates, dichromates, andsulfates are preferred for their sensitivity and solubility. Oxides mayalso be used but oxides are not as convenient as the other compoundsbecause of their low solubility. Mixtures of various detonationcatalysts are also contemplated. One especially preferred detonationcatalyst is copper chloride. From 0% up to about 5% by weight of theexplosive composition of this second category of sensitizing agents canbe employed in the explosive emulsions of the present invention. Thesoluble detonation catalysts can be added by admixing same with theinorganic oxidizing salt solution. Relatively insoluble oxide detonationcatalysts can be added to the emulsion matrix.

The low water emulsion explosive compositions of the present inventionalso employ a third category of sensitizing agents in the form of closedcell void containing materials. Such materials can include anyparticulate material which comprises closed cell, hollow cavities. Eachparticle of the material can contain one or more closed cells, and thecells can contain a gas, such as air, or can be evacuated or partiallyevacuated. Sufficient closed cell void containing materials should beutilized to yield a density of the resulting emulsion of from about 0.9to about 1.3 grams/cc. Generally, from about 0.25% to about 10% byweight of the explosive emulsion composition of such materials can beemployed for this purpose.

The preferred closed cell void containing materials used in thecompositions of the subject invention are discrete glass spheres havinga particle size in the range from about 10 to about 175 microns. Ingeneral, the particle density of such bubbles can be within the range ofabout 0.1 to about 0.7 grams/cc. Some preferred types of glassmicrobubbles which can be utilized within the scope of the subjectinvention are the microbubbles sold by 3M Company and which have aparticle size distribution in the range of from about 10 to about 160microns and a nominal size in the range of from about 60 to 70 microns,and densities in the range of from about 0.1 to about 0.4 grams/cc.Preferred microbubbles sold by 3M Company are distributed under thetrade designation B15/250. Further examples of such materials includethose sold under the trade designation Eccospheres by Emerson & Cumming,Inc. and which generally have a particle size range of from about 44 toabout 175 microns at a particle density of about 0.15 to about 0.4grams/cc. Microbubbles sold under the designation Q-Cell 200 byPhiladelphia Quartz Company are also suitable. When glass microbubblesare employed in the compositions of the subject invention, they cancomprise from about 1% to about 5% by weight thereof.

Auxiliary fuels can also be employed. An excellent auxiliary fuel, whichis nonexplosive, is particulate aluminum. Aluminum, and othernonexplosive auxiliary fuels, can be employed in amounts ranging fromabout 0% to about 20% by weight of the emulsion explosive composition.Of course, the second category of sensitizing agents discussed abovealso act as auxiliary fuels because of their negative oxygen balance.

The low water explosive emulsions of the subject invention can beprepared by premixing the water and inorganic oxidizer salts in a firstpremix, and the carbonaceous fuel and emulsifier in a second premix. Thetwo premixes are heated, if necessary. The first premix is generallyheated until the salts are completely dissolved (about 120° to about220° F.) and the second premix is heated, if necessary, until thecarbonaceous fuel is liquefied (generally about 120° F. or more if waxmaterials are utilized). The premixes are then blended together andemulsified to form the emulsion matrix and thereafter the glassmicrobubbles, or other gas entrapping materials are added until thedensity is lowered to the desired range. In the continuous manufactureof emulsion explosive compositions, it is preferred to prepare anaqueous solution containing the oxidizers in one tank and to prepare amix of the organic fuel components (excluding the emulsifier) in anothertank. The two liquid mixes and the emulsifier are then pumped separatelyinto a mixing device wherein they are emulsified. The emulsion matrix isnext pumped to a blender where the glass microbubbles and insolubleauxiliary fuel, if desired, are added and uniformly blended to completethe water-in-oil emulsion explosive product. The resulting emulsionexplosive is then processed through a Bursa filler or other conventionaldevice into packages of desired diameters. For example, the emulsionexplosives can be packaged in spiral wound or convoluted polymerlaminated paper cartridges.

The following examples are given to better facilitate the understandingof the subject invention but are not intended to limit the scopethereof.

Examples set forth in Table I below were prepared in the followingmanner. A first premix of water and the inorganic oxidizers was preparedat about 220° F. A second mix of the carbonaceous fuel and theemulsifier was prepared at a temperature of about 150° F. The firstpremix was then slowly added to the second premix, with agitation, toobtain a water-in-oil emulsion. Thereafter, the glass microbubbles wereblended into the emulsion to form the final emulsion explosivecomposition.

                  TABLE I                                                         ______________________________________                                               Compositions                                                           Ingredients                                                                            1      2      3    4    5    6    7    8                             ______________________________________                                        Water    8.0    6.0    8.0  8.0  8.0  8.0  8.0  8.0                           Wax      3.0    3.0    3.0  3.0  3.0  3.0  3.0  3.0                           Oil      1.0    1.0    1.0  1.0  1.0  1.0  1.0  1.0                           Emulsifier                                                                             1.0    1.0    1.0  1.0  1.0  1.0  1.0  1.0                           Ammonium 62.0   64.0   64.0 67.0 62.0 69.0 68.5 66.5                          Nitrate                                                                       Sodium   10.0   10.0   10.0 10.0 13.0 10.0 12.0 10.0                          Nitrate                                                                       Ethylene-                                                                              10.0   10.0   10.0 5.0  10.0 5.0  2.5  7.5                           diamine                                                                       dinitrate                                                                     Copper   3.0    3.0    1.0  3.0  --   1.0  2.0  1.0                           Chloride                                                                      Glass    2.0    2.0    2.0  2.0  2.0  2.0  2.0  2.0                           Microspheres                                                                  Density  1.18   1.18   1.17 1.18 1.17 1.16 1.17 1.18                          g/cc                                                                          1/2 Cart-                                                                              5      4      5    4    3    3    3    3                             ridge Gap                                                                     sensitivity                                                                   (inches)                                                                      ______________________________________                                    

All of the compositions set forth in Table I were extruded or tampedinto paper tubes having a 11/4 inch diameter, and sealed. The cartridgeswere then cut in half and tested according to the regulations set forthin 30 CFR 15 et seq., the standards used by the Bureau of Mines todetermine the 1/2 cartridge gap sensitivity of permissible typeexplosives.

While the subject invention has been described in relation to itspreferred embodiments, it is to be understood that various modificationsthereof will be apparent to those of ordinary skill in the art uponreading the specification, and it is intended to cover all suchmodifications which fall within the scope of the appended claims.

We claim:
 1. A cap-sensitive water-in-oil explosive emulsion compositionhaving a 1/2 cartridge gap sensitivity of at least about three inchesformed from an emulsion matrix having from about 4% to less than 10% byweight water.
 2. The water-in-oil emulsion explosive composition ofclaim 1 wherein from about 65% to about 85% by weight of the totalcomposition is inorganic oxidizing salts, from about 3.5% to about 8% byweight of the total composition is carbonaceous fuels, including anemulsifier and from about 0.25% to about 10% by weight of the totalcomposition is closed cell void containing materials.
 3. The explosivecomposition of claim 2 and further comprising a sensitizing agentselected from the group consisting of lower alkylamine and alkanolaminenitrates.
 4. The explosive composition of claim 3 wherein saidsensitizing agent comprises up to about 20% by weight of said explosiveemulsion.
 5. The explosive composition of claim 2 and further comprisinga detonation catalyst selected from the group consisting of watersoluble nitrate, halide, chromate, dichromate, and sulfur compounds inwhich said compound contains a metal selected from the group consistingof aluminum, magnesium, cobalt, nickel, lead, silver, mercury, copper,zinc, iron, and chromium.
 6. The explosive composition of claim 5wherein said detonation catalyst comprises up to about 5% by weight ofsaid explosive emulsion.
 7. The explosive composition of claim 2 andfurther comprising up to about 20% by weight of the total compositionauxiliary fuels.
 8. The explosive composition of claim 7 wherein saidauxiliary fuel is particulate aluminum.
 9. The explosive emulsion ofclaim 2 wherein the emulsifier present in said carbonaceous fuels is inthe range of from about 0.5% to about 2.0% by weight of said explosiveemulsion composition.
 10. The explosive composition of claim 2 whereinsaid inorganic oxidizing salts comprise from about 55% to about 70% byweight of the composition of ammonium nitrate, from about 5% to about20% by weight of the composition of sodium nitrate and from about 0% toabout 20% by weight of the composition of ammonium perchlorate.
 11. Theexplosive composition of claim 2 wherein said carbonaceous fuelcomprises water immiscible emulsifiable material selected from the groupconsisting of petrolatum, microcrystalline, paraffin, mineral, animal,and insect waxes, petroleum oils, vegetable oils and mixtures thereof.12. The explosive composition of claim 2 wherein said closed cell voidcontaining material is glass microbubbles and is present in an amount offrom about 1.0% to about 5% by weight of the total composition.
 13. In acap-sensitive water-in-oil explosive emulsion comprising a discontinuousaqueous oxidizer salt solution phase, a continuous carbonaceous fuelphase, and closed cell void containing materials, the improvementcomprising:employing an aqueous oxidizer salt solution having less than10% water, by weight of the emulsion matrix of the composition, tothereby substantially increase the 1/2 cartridge air gap sensitivity ofsaid explosive emulsion.
 14. The improved explosive composition of claim13 wherein water is present in said matrix in an amount of from about 6%to about 8% by weight.
 15. The improved explosive composition of claim13 wherein said carbonaceous fuel phase, including an emulsifier, ispresent in an amount of from about 3.5% to about 8% by weight of thetotal composition.
 16. The improved explosive composition of claim 13wherein said closed cell void containing materials are present insufficient amounts to obtain a density of from about 0.9 to about 1.3g/cc for the total composition.
 17. The improved explosive compositionof claim 13 wherein said closed cell void containing materials arepresent in an amount of from about 0.25% to about 10% by weight of thetotal composition.
 18. The improved explosive composition of claim 13wherein said carbonaceous fuel phase includes a water-in-oil emulsifierin an amount of from about 0.5% to about 2.0% by weight of the totalcomposition.
 19. The improved explosive composition of claim 13 whereinthe inorganic oxidizing salts contained in said discontinuous aqueousoxidizer salt solution phase comprise from about 55% to about 70% byweight of the total composition of ammonium nitrate, from about 5% toabout 20% by weight of the total composition of sodium nitrate and fromabout 0% to about 20% by weight of the total composition of ammoniumperchlorate.
 20. The improved explosive composition of claim 13 andfurther comprising from about 0% to about 20% by weight of the totalcomposition of a sensitizing agent selected from the group consisting oflower alkylamine and alkanolamine nitrates.
 21. The improved explosivecomposition of claim 13 and further comprising from about 0% to about 5%by weight of the total composition of a detonation catalyst selectedfrom the group consisting of water soluble oxide, nitrate, halide,chromate, dichromate, and sulfur compounds in which said compoundscontain a metal selected from the group consisting of aluminum,magnesium, cobalt, nickel, lead, silver, mercury, copper, zinc, iron,and chromium.
 22. The improved explosive composition of claim 13 andfurther comprising from about 0% to about 20% by weight of the totalcomposition of an auxiliary fuel.
 23. The improved explosive compositionof claim 22 wherein said auxiliary fuel is particulate aluminum.